This brings nikolaymihaylov/AR.js/dev up-to-date with the original
branch jeromeetienne/AR.js/dev

Added NPM, Gitter, twitter, patreon badges

Conflicts:
	babylon.js/README.md
	babylon.js/src/babylon-ar.js
	contribs/portableAR.js/build/portable-ar.js

Conflicts:
	aframe/build/aframe-ar.js
	aframe/src/component-anchor.js

fix custom marker

Update aframe README to include information about a-marker's 'emitevents' property. Add a link to the example of its usage.

Add 'emitevents' property to the arjs-anchor component, which emits events when a marker is found and when it is lost.

Added an image at the top, removed Efficient from the title.

Created CONTRIBUTING.md